Process and apparatus for press-forming and quenching a steel stock

ABSTRACT

The invention relates to a process and apparatus for pressforming and quenching a steel stock such as diaphragm spring for automotive clutch use. In the invention, the stock is preparatorily heated to its austenitizing temperature such as about 800* C., or so, placed on one of two cooperating die elements, and then squeezed therebetween under pressure, said die elements having working surfaces having corresponding dimensions and configurations so as to be brought into a pressurized and heat-conducting contact with the to-be-quenched zone of said stock, thereby said stock being press-formed to its desired shape and wholly or locally quenched to a desired hardness such as HRC 60* by conducting substantial amount of heat from the stock to the die elements.

United States Patent Komatsu et a1. 14 1 June 13, 1972 [54] PROCESS ANDAPPARATUS FOR [56] References Cited PRESS-FORMIN G AND QUENCHING AUNITED STATES PATENT 5 STEEL STOCK 2,118,018 7/1938 Swanson ..72/342[72] Inventors: Nobnru Ko-masu; Takatoshi s I i; 2,983,503 5/1961Haussermann ..29/ 173 1,457,772 6/1923 Forsyth ..148/12.4 2 744 7465/1956 Batz ..14s/12.4 Hara, Chiryu-machi, Hekikai-gun; Koulchi AsakuraKanya'sh" an of Japan Primary Examiner-Lowell A. Larson 731 Assignees:Kabushiki Kaisha Toyota Chuo-Ken- Mama-411%,RmhWelLMim, & Macpeakkyusho; Aisin Seiki Company Limited, Aichi-ken, Japan [57] ABSTRACT IThe invention relates to a process and apparatus for pressforming andquenching a steel stock such as diaphragm spring Flledi 1970 forautomotive clutch use. In the invention, the stock is J 50 preparatorilyheated to its austenitizing temperature such as [211 No about 800 C orso, placed on one of two cooperating die elements, and then squeezedtherebetween under pressure, said [30] Foreign Application Priority Datadie elements having working surfaces having corresponding 7 dimensionsand configurations so as to be brought into a pres- Jan. 25, JapanSurized and heabconducting Contact i h the to be quenched 7 zone of saidstock, thereby said stock being press-formed to its [52] U.S.Cl..72/342, 29/173, 148/ 12.4 desired Shape and wholly or locally quenchedto a desired [5 1 Int. Cl. t l hardness uch as HRC 60 conductingsubstantial amount of [58] Field Of Search ..72/342; 29/173; 148/12.4,131 heat from the stock to the die elements,

8 Claims, 10 Drawing Figures 'PATENTEDJuu 13 1912 3.668.917

sum 1 or 5 l l I l 2 3.3 4 6 8 I0 THERMAL CAPACITY RAT|O= THERMAL CAP.OF COOLING TOOL THERMAL CAP. OF STOCK TO QUENCHD I PATENTEDJum I972 Isum 0F 5 FIG. 5

Cu f 500 RATE,

THERMAL PENETRATION SANDSTONE "1 SCM4 SCr4 M8 IDIAL CRITICAL DIAMETER Dinch F I G. 8

E I 68 2J0 3 2.08 g i 66 CL 5 2.06 3 w 64 LU g 2.04 -5 62 2 E 60 2.02 5,3 g HARDNESS AFTER QUENCHING 200 L 58 0 0 H THICKNESS OF SAMPLE 2 L98 8z 56 UPON TREATED T 2 Q L96 x E 54 i I 1- 2 4 68m 20 60 I00 200400 I0002000 10000 PRESSURE APPLIED ON SAMPLE, KGS. PER SQ. CENTIMETER TREATED,MM

PATENTEBJUMa I972 3.668.917

SHEET 50F 5 FIG. 9

-,NO- U O3\1 0 GOO GOO l I I: l l

I 63' I I I O 1.

HARDNESSAFTER QUENCHING, HRC

l l l l l l l s sao 70 60 50 40 3o 20 IO 9 OUTSIDE CENTER PERIPHERYMEASURING POSITIONS,

- MEAS'D IN MM FROM CENTER OF THE STOCK thus an additional and tediousstep such as hammering, tempering or the like must be employed forremoving such PROCESS AND APPARATUS. FOR PRESS-FORMING AND QUENCIIING ASTEEL STOCK This invention relates generally to certain improvements inand relating to the press-forming and quenching techniques; It relatesto more specifically to a process for press-forming and quenching steelsheet products and an apparatus adapted for carrying out said process.

According to the prior technique, steel sheets intermediate or finalproducts, as the case may be, are manufactured in successive andseparate steps of press-forming and quenching. As is commonly known, thequenched products may frequently represent considerable distortion fromthe desired shape and pressdistortion developed in the quenching step.Invitation of the distortion after quenching will naturally reduce thedegree of precision in shape and dimension of the products.

It is therefore the main object of the invention to provide a process,as well as an apparatus for press-forming and quenching steel sheetproducts, capable of obviating the-conventional, drawback ofnecessitating the aforementioned kind of additional correction servicesuccessive to the quench step.

A further object is to provide a process as well as an apparatus of theabove kind, capable of improving the degree of precision in shape anddimension of the quenched products in spite of the omission of theconventionally adopted correction service.

For attaining the aforementioned several objects, it is now proposed toplace a steel stock between a pair of cooperating dieelements uponheating said stock to its austenitizing temperature and to providepressure upon said stock and at the same time rapidly to conduct heatfrom said stock to said die elements by keeping the latter at a coolingtemperature during the whole' processing, thereby a quench effect uponsaid stock under forming'pressure.

An apparatus for carrying out the above process, comprises an upper dieelement having a working surface made in registration with thecorresponding finished surface of the steel stock, a lower die elementhaving a working surface made in registration with the correspondingfinished surface of the stock; an actuating power means for moving saiddie elements towards each other and separating from each other, forapplying a mechanical pressure upon said stock when the latter issqueezed between said die elements when said actuating means is broughtinto actuation in the direction towards relative engagement of the dieelements; and cooling means for said die elements, thereby said stockbeing subjected to cooling for quenching as well asforrning to itsdesired shape when squeezed between the cooled die members underpressure.

' The actuating means is preferably shaped into a hydraulicpiston-and-cylinder unit operable by the will of an operator, either ofsaid piston or cylinder being mechanically connected 7 with one of saiddie elements for driving them as desired for the press-forming andquenching job. The cooling means is preferably formed into a coolingchamber provided in each of the die elements and arranged to receiving acirculating stream of coolant.

These and further objects, features and advantages of the invention willbecome more apparent when read the following detailed description of theinvention by reference to the accompanying drawings.

In the drawings FIG. 1 is a top plan view of a diaphragm spring destinedfor use in an automotive clutch assembly, and indeed, as arepresentative example of the products manufactured according to theimproved technique proposed by the invention.

' FIG. 2 is a side view of the diaphragm spring shown in FIG. 1.

FIG. 3 is an elevational view of an apparatus adapted for use in thepractice of the process according to the invention.

FIG. 4 is an enlarged sectional elevation of several main workingelements of the apparatus shown in FIG. 3.

. free ends 103 of all the lever portions 102 when It will be clearlyseen from the foregoing description and by judgement from the drawingthat the diaphragm spring 100 FIG. 5 is an explanatory chart in whichthe thennal penetration rate, Kcal/mPC'h, of the tool has been plottedagainst the ideal critical diameter in inches, of the work, as arepresentative example in the practice of the process according to thisinvention.

FIG. 6 is a further explanatory chart showing the relationship betweenthe theoretical final temperature, C., attainable in the work uponquenching, on the one hand, and the thermal capacity ratio which meansmore specifically the relative ratio between the thermal capacity of theand that of the work to be quenched.

FIG. 7 is a still further explanatory chartillustrative of therelationship between the hardness of quenched work samples as processedby the process according to the invention and the I thicknesses of thesamples.

FIG. 8 is a still further explanatory chart illustrative of theinfluence upon the hardness as well as the thickness of the productprocessed in accordance with the invention, by the processing pressure.

FIG. 9 is a similar view to FIG. 4, wherein a selectively localizedquenching is being carried into effect as a modified mode of the processaccording to this invention.

FIG. 10 is a still further explanatory chart illustrative of adistributed hardness developed on the surface of .a work piece processedin accordance with the modified mode of the invention shown in theforegoing FIG. 9.

Referring now to FIGS. I and 2 of the drawings, the kind and nature of arepresentative work piece, or more specifically diaphragm spring forautomotive clutch use and the conventional technique of thepress-forming and the quenching thereof will be briefly described forthe illustration of technical background of the present invention.

The diaphragm spring 100 has a generally dish-shaped configuration andcomprises a peripheral ring-shaped main spring body part 101 and anumber of radially arranged lever-like portions 102 which extendconcentrically from said main body part 101 towards the center of thediaphragm when seen in its top plan view shown in FIG. 1. Each of saidlever-like portions 102 has a gradually reducing width and there is anopen circular area defined by a circle connecting the innermost or topseen in FIG. 1.

represents a rotational symmetry about its central axis and hasgenerally a truncated cone shape. The diaphragm spring is made generallyof a kind of high carbon steel and the lever ends 103 must be hardenedso as to provide a possible minimum sliding wear in sliding contact witha conventional automotive clutch release bearing not shown, while theremaining parts of the diaphragm spring must have generally a springcharacteristic as such. In order to satisfy the aforementioned specificrequirements, the diaphragm spring is manufactured through the followingseveral successive fabricating steps:

a. a generally circular stock is pressed out from a large size steelsheet material, so as to represent a number of leverlike portions 102and a ring-shaped main body part 101 integral therewith.

b. the thus pressed-out plane stock is shaped generally into a truncatedcone on a forming press.

c. the thus shaped truncated cone stock is heated at about 830 C. forabout 20 minutes and then quenched therefrom into an oil bath forhardening of the product as a whole.

d. the quenched .stock is then heated at about 320 C. for

about minutes and then air-cooled to normal temperature for performing aprovisional tempering.

e. the thus provisionally tempered stock is heated at about tool toprovide quenching g. the lever portions are subjected to a temperingstep.

It may be therefore understood that according to the prior technique forthe manufacture of the diaphragm spring of the above kind, the wholeprocess requires a longer treating period, as well as a highly skilledworkmanship, on account of separately applied quenching and repeatedlyapplied tempering steps, as specifically appearing in the foregoingitems c e and especially for the purpose of removing unavoidablydeveloped thermal deformation.

It is proposed by the present invention to carry out several processingsteps as at b e, beginning from the press-forming and ending with thedeformation removing tempering, exclusively in one step and in ashortest possible time period in such a way that a steel stock pressedout from a sheet material and heated up to a quenching temperature issubjected to a press fonning step while being held in position by meansof die members providing in combination the final space configuration ofa desired product, thereby transmitting heat from the stock to the diemembers for quenching the stock simultaneously with the press-formingthereof to its final configuration.

Next, referring to FIGS. 3 and 4, a preferred apparatus adapted forcarrying out the process will be described in detail.

In these figures, the numeral denotes a bed which is provided with aplurality of legs 11 mounted in position on a floor surface 12. Aplurality of vertical columns 13 are rigidly attached with their lowerends to the bed 10 and a rigid top plate 14 is fixedly attached to theupper ends of said columns. A hydraulic cylinder 15 is rigidly mountedon the plate 14 although the fixing and attaching means have beenomitted from the drawing on account of its very popularity. The interiorcylinder spaces 22 and 23 defined by a piston 24 slidably received inthe cylinder 15 are connected through respective pipings 16 and 17 and acontrol valve assembly 18 to a certain conventional hydraulic pressuresource, such as pressure oil reservoir, oil pump or the like, not shown.Control valve 18 is so designed and arranged that by manipulating acontrol lever 19 attached thereto, pressure oil flow through thesepipings I6; 17 can be on off controlled for supply and discharge of oilto and from the cylinder 15.

A slide or ram 20 formed into a horizontally extending rigid plate isformed with a plurality of tubular members 21 which are slidably mountedon said columns 13.

The hydraulic cylinder 15 is provided with an upper cover flange 15a anda lower cover flange 15b rigidly attached by means of a plurality offixing bolts, not shown only for simplicity of the drawing, for sealingthrough suitably designed and arranged conventional gasket means, notshown, the cylinder spaces 22 and 23, and the piston 24 is rigidlyconnected with a vertically extending piston rod 25 which is in turnrigidly connected at its lower extremity with the ram 20, although thefixing means have not been shown only for simplicity. Therefore, theassembly comprising piston 24, rod 25 and ram 20 is slidably movable inthe vertical direction, as hinted by a small double head arrow 25' shownin FIG. 3 by pressurizing the hydraulic working liquid medium such asoil prevailing in the upper or lower cylinder chamber 22 or 23 byproperly manipulating the control valve 18 as conventionally.

A holder plate 26 is fixedly attached by means of a plurality of fixingscrews 27 on the bottom surface of the ram 20, and carries an upper dieelement 28 rigidly attached by means of fixing screws 29 to the holder26, said die element being shaped into substantially a stepped hollowcylinder. The die member 28 is formed in the bottom wall with apositioning recess 129 which is so designed and arranged to cooperatewith a mating pin 30, as will be more fully described hereinafter. Theinterior space 28a of die member 28 is closed by means of a closureplate 31 which is sealingly attached through a seal ring 32 by means ofa plurality of fixing bolts 33 to a shoulder surface 34 formed on aupper part of the die member 28. The bottom surface 28b around saidpositioning recess 129 is shaped into a tapered ring surface adapted toshape the inside truncated cone surface of the product diaphragm spring40. The thus sealingly closed interior space 28a of the upper die memberserves as a cooling liquid space wherein a coolant, preferably coldwater, is supplied through a flexible tubing 43 and let out through aduct 133 bored laterally through the upper part of the die wall; aflexible tubing 34 connected at its one end fixedly to said duct 133;and a piping 35 connected rigidly with the opposite end of said tubing34.

A lower holder plate 38 which is similar in its design and function withthe upper holder plate 26, is fixedly attached by screws 37 to the baseor bed 10, on its upper surface 1011 as shown more specifically in FIG.4, said plate 38 mounting in turn fixedly by means of a plurality offixing screws 39 a lower die member 36 which is shaped substantiallyinto an inverted cylindrical cup, the interior inside space 360 beingsealingly closed by a closure plate 49 similar to the upper closure 31.This plate 49 is fixedly attached through the intermediary of seal ring44 by set screws 48, the thus sealingly closed interior space 36aserving again as a cooling liquid chamber as in the case of upper diechamber 28a. The upper or working surface 36b of the lower die member 36has a general configuration mating with that 28b of the upper die member28 and is formed with a central recess 1360 which receives snugly thepositioning or centering round pin 30 for a processing work piece 40,the latter being formed with a central opening 40a for slidablyreceiving said pin.

The lower die member is formed with a duct 134 which is bored throughthe lower part of the peripheral wall of the die 36 to which is fixedlyattached a coolant supply piping 42 leading to a supply source, notshown. A control valve 45 is inserted in this piping 42 for control ofproper supply quantity of the coolant which is preferably cold water.Both cooling chambers 28a and 360 are kept in fluid communication witheach other by means ofa flexible tubing 43 which is connected at itsrespective ends with said chambers, as most clearly seen from FIG. 4.

In the following, a process for the simultaneous press-forming andquenching operation according to the invention will be described indetail, in conjunction with the operation of the press so far shown anddescribed with reference to FIGS. 3 and 4.

The processing stock 40 or diaphragm spring stock, had an outsidediameter of mm and a thickness of 2 mm. The material of the stock wascarbon tool steel, class 5 (HS, SK-S), while that of the dies 28 and 36was structural carbon steel (.IIS, 545C). The term JIS" is anabbreviation of Japanese Industrial Standard."

The flat diaphragm spring stock was heated in a suitable furnace or thelike at a austenitizing temperature of about 830 C.; promptly taken outfrom the furnace and then placed on the lower die 36 with itspositioning pin 30 brought into registration with the central roundopening 40a of the stock 40. Next, the control valve 18 is actuated soas to introduce the pressurized working liquid through the piping 16into the upper cylinder space 22 for forcibly lowering the ram assemblycomprising piston 24, rod 25, ram plate 20, upper holder plate 26 andupper die 28, towards the lower die 36, thereby bringing the stock intoits squeezed position between the both die members under high pressure.At this pressing and quenching stage, the upper surface of the stock isbrought into pressure engagement with the working surface of the upperdie and in the similar way the bottom surface of the stock is broughtinto pressure contact with the working surface of the lower die. In thisway, the stock is forcibly transformed from its plane configuration intothe final or substantially truncated cone shape shown in FIG. 2. At thesame time, substantial heat is discharged from the stock and penetratethrough the walls of the respective dies into the circulating coolingmedium, preferably cold water and was carried along thereby. In thisway, the stock was press-formed to the desired shape and at the sametime quenched in an effective manner.

The die-application pressure acting upon the stock may be varied fromabout 6 to 2,000 kgs. per sq. cm according to the size and dimensions ofthe stock to be treated. Therefore, the

' penetration rate of the pressing and quenching dies, the highercooling rate of the treating stock must be expected. Next, it should benoted that the temperature, T, as observed at the contacting surfacewhich is deemed to establish at an instant when two bodies havingdifferent temperatures are brought into physical contact with eachother, can be determined by the following formula where T, and b,represent the initial temperature and thermal penetration rate of onebody, respectively; and T and b stand for those of the other body,respectively.

. As an example, consider such a case where a treating stock of carbonsteel, heated up to 800 C. T, is to be quenched. In this case, what kindof material and what rate of thermal penetration should be selected forthe quenching dies? Then, the following calculation can be performed Thethermal penetration rate (b,) for carbon steel may be safely taken asabout 200 l(cal/m*-"C-h" and the temperature (T,) of the cooling toolmeans may be assumed to be 20 C. If the steel is quenched beyond theperlite transformation temperature of steel (which meansthe nosetemperature on S- curve of steel), about 500 C. T, instantly uponcontact of the steel with the quenching tool, the desired quench effectmay definitely be introduced. When these values are introduced in theabove formula 1, then b I25 (Kcal/m 'C-h" Thus, the tool materialhaving'larger value of thermal penetration' rate than the abovecalculated value of b will serve for the desired purpose. From observingthe chart shown in FIG. 5, it will be seen that copper, silver and ironhave larger thermal penetration values than that above specified. Thus,it can be concluded that any one of the above specified several metalswill serve well for the quenching purpose. In the above calculation,however, thermal resistance between the contact- .ing surfaces andthehardenability of the kind of alloy have been neglected. In fact,however, it can not be always said that the quenching effect isintroduced depending exclusively upon the surface temperature of thetreating stock upon contact with the quenching tool, wherein the abovekind of contacting thermal resistance, the hardenability of the treatingstock and the size or thermal capacity of the treating stock must benecessarily taken into account. In FIG. 5, experimental results areshown, illustrative of the relationship of the thermal penetration rateb and the hardenability (represented by ideal critical diameter D, withlarger value of this diameter, the hardenability will be correspondinglyhigh) relative to the size of the treating stock.

On the chart shown in FIG. 5, the curve (A) shows the relationshipbetween the necessary heat penetration rate (several representativematerials being specified in their order of thermalpenetration ratealong the axis of ordinates) and the kind of the material in case ofquenching treatment of a steel plate having 2 mm thickness. As anexample, when a plate made of JIS, 845C (D, nearly equal to 0.8 in;thickness being 2 mm) is to be quenched, the thermal penetration rate ofthe cooling die may be determined as b 200 by observing said curve (A).

Thus, when quenching a plate made of this kind of steel and having athickness of 2 mm, the value of heat penetration rate higher than 200will suffice for the desired purpose and the quenching material may beFe, Al or Cu. It will be seen that in this case, the desired quenchingcan be realized by adopting any selected combination from the area abovethe curve (A). In the similar way, the area above the curve (B) showsvarious combinations for allowing a quenching of steel plate, 6 mmthick. The area above the curve (C) shows in the similar way variouscombinations for allowing a quenching treatment of a 25 mm-thick steelplate. Non-ferrous material such as aluminum shows a similar tendency asabove specified.

As for the thermal capacity (specific heat multiplied by weight),Kcal/C, the quenching may be more easily carriedinto effect with higher-value thereof owned by the cooling material than that of the treatingstock.

The attainable final temperature T(C.) of the treated stock can becalculated from the following fon'nula where, C, stands for thenecessary minimum thermal capacity of the treating stock;

T, represents the initial temperature of the stock;

T stands for the initial temperature of thecooling material;

and

C represents the thermal capacity of the same material.

When considering a representative case wherein a steel stock is quenchedby contact .with a solid cooling material, the theoretically attainablefinal temperature of the stock upon contact with the quenching materialmust be lower than the transformation starting temperature ofmartensite, or Ms point. In the case of quench treatment of a steelhaving a Ms point of 200 C. T), from a temperature of 800 C. T,), andassuming that the temperature of the stock to be quenched is at 20 C. T,the ratio C /C, will be nearly equal to 3.3 when introducing thesevalues into the above formula (2). In order to bring the temperature ofthe stock by a quenching contact of the above nature, to a value lowerthan Ms point, the thermal capacity of the quenching materialmust be atleast 3.3 times thatof the treating stock. When the attainable finaltemperature of the stock is plotted against the relative ratio betweenthe thermal capacity of the stock and that of the quenching material, acurve will be obtained as shown, by way of example, in FIG. 6. Ms pointsfor several preferred materials are also shown along the axis ofordinates.

In the following, several specific features will be described based uponthe practical experiments. In these experiments, the forming andquenching tools were of structural carbon steel, JIS, S45C.

In FIG. 7 several comparative curves are shown. The stock materials wereJIS, 845C and JIS, SCM 4, the latter being chromium-molybdenum steel,class 4. When the quenched hardness is set to l-I C 55, the hardenablethickness of steel plate stock amounted to similar or even higher valuethan those obtainable with the conventional oil quenching process. Inthe comparative tests shown in FIG. 7, samples were quenched from 850 C.by the process according to this invention, and comparison is made withthe oil quenched results. The quenched hardness was plotted against thethickness of the sample. It will be seen from the chart, about 8 mmthick samples of JIS, 845C and those about 16 mm thick of JIS, SCM 4could be effectively quenched according-to this invention.

As seen from a further chart shown in FIG. 8, a considerably wide rangeof die applying pressure can be employed in the practice of theinventive quenching process for realizing ,an evenly distributed quenchhardness and a specific thickness of the sample which was in this case adiaphragm spring for automotive clutch use, as was already referred tohereinbefore.

In this chart, the quenched hardness was plotted against thedie-applying pressure. At the right-hand side and along the axis ofordinates, the final thicknesses of the quenched samples are shown.

As seen, the die-applying pressure necessary for obtaining an evendistribution of quenched hardness amounts to 6 kgs. per sq. cm. orhigher. On the other hand, the die applying pressure necessary forproviding an even thickness of the quenched steel sheet stock rangesfrom nil to 2,000 kgs. per sq. cm. which means a considerably widerange. It is naturally recommendable to adopt, out of the abovespecified pressure range, a possible minimum, yet enough large pressurefor attaining the desired press-forming effect of the processed workpiece. If, however, a reduction in the thickness of the steel sheetstock during the press-forming and quenching process is allowable to acertain degree, or alternatively a reduction in the thickness of theprocessing stock is desired rather in a positive way, the die-applyingpressure range above specified would have a minor importance.

In the following table, a comparative test result is shown in terms ofthe difference in lever end height as a measure of developed quenchdistortion in the quenched steel products, more specifically diaphragmsprings for automotive clutch use, which have been processedcomparatively according to the prior art oil quenching process and thepress-forming and quenching process proposed by the invention. It hasbeen found that the product processed in accordance with the inventionrepresents only one-eighth one-fourth those encountered withconventional quenching processes.

irregularity in Height at irregularity in Kind of quenching Height atInner Remarks: the above figures were taken as the mean valves of 50test samples in each case. 50

The irregularity in height at outside periphery of the product asspecified above was measured in such a way that the product diaphragmspring was placed on a surface plate and the local gaps between theperipheral bottom surface of the diaphragm and the surface plate wereprecisely measured. When the gap was measured to nil, it was assumedthat there was no quench distortion. On the other hand, the irregularityin height at inner lever ends was determined by the difference in heightbetween the highest lever end and the lowest lever end. When thedifference be nil, the quench distortion in this respect was assumedalso to be nil.

In the following, we will compare the inventive process with theconventional process in relation to the thermal cycle.

The comparative conventional process comprises the fol lowing fourprocessing steps in succession:

press-forming a plane diaphragm spring stock so as to the desiredtruncated cone shape;

heating the press-formed stock at about 830 C. for about minutes andimmersing it in a oil bath for quenching; heating the quenched stock atabout 320 C. for about 90 minutes and then air-cooling it to normaltemperature, for reducing the hardness to a certain small degree; andheating the thus treated stock while forcedly kept in position, byapplying jig means thereon to, at about 450 C. for about I80 minutes andthen air-cooled to normal temperature for tempering to relieve ofquenching distortion.

According to the quenching process proposed by the invention, the planestock is heated at about 830 C. for about 20 minutes and then squeezedbetween a pair of press-forming dies for quenching as well aspress-forming the stock. The thus quenched and press-formed stockrepresents only a smallest possible quench distortion, as was enlisted,by way of example, in the foregoing table, thus practically obviating anadditional and separate distortion-relieving step normally andconventionally employed. It is only necessary to heat the quenched stockat about 450 C. for about minutes and then aircooled to normaltemperature, for attaining a tempering effect, thereby the whole processconsisting of only two heattreating steps and improving the overallthermal efficiency.

According to our practical experiments, it has been found that the novelteaching proposed by the'invention may be carried into effect in such away that the steel stock is pressformed and at the same time locallyquenched.

A modified embodiment of the process as well as the apparatus accordingto this invention will be described by reference to FIGS. 9 and 10.

In this case, a diaphragm spring stock 40 destined for automotive clutchuse and prefabricated from a steel sheet, 2 mm thick, the material steelbeing carbon tool steel, Class 5, in conformity to the specifications ofJIS, SK-S as before, was processed on a modified machine shown in FIG.9. The processing was so carried out that it was pressed fonned to thedesired final shape of a truncated cone in its elevationalconfiguration, while at the same time the stock is subjected onlylocally at the peripheral ring-shaped area 101 (FIG. 2) as definedtherein by an imaginary dotted circle 104, and extending outwardlytherefrom.

For this purpose, the upper and lower die elements 28 and 36 are formedwith respective mating working surfaces 28b and 36b having more limitedareas than before adapted for performing the desired local quenchingfrom both upper and lower sides of the peripheral ring-shaped zone ofthe stock, the remaining working surface of each of said dies beingsubstantially recessed at 28a or 36d, respectively, for avoiding thestock from any physical contact with the press dies.

The processing particulars in this case were same as before. Morespecifically, the diaphragm spring stock 40' was heated to a quenchingtemperature as before and then placed on the lower die element 36'around its centering pin 30 and the upper die element 28' was loweredhydraulically as before against the lower die element through theintermediary of the thus centrally positioned processing stock.Naturally, in this case, the outer ring peripheral zone 101' of thestock was brought into heat-conducting pressure contact with therespective working surfaces 28b and 3611', the remaining area of thestock being prevented from contact with the pressing and quenching dieelements, as was briefly described hereinabove. In FIG. 9, the thuscontacted ring are 101' being shown at y, while the remainingnon-contacting zone being denoted by x. In this way, the contacted andpressurized area y" was only quenched, while the remainingnon-contacting area .r" was subjected in noway to the quenching effect.

FIG. 10 represents a curve showing a distribution of the hardness afterquenching in the thus treated stock. As clearly seen from this curve,the outer peripheral zone 101' of the stock 40', said zone having aradial length y" as said above, is subjected to a substantial quenchingamounting to about H C 65, while the remaining non-contacted area,having a radial length of x", has not been quenched, representing in themean a hardness of about H C 30. The temperature from which the stockwas quenched was 830 C. as mentioned hereinbefore.

In this way, the stock was press-formed and at the same time effectivelyquenched.

From the foregoing, it may well be understood that the process accordingto this invention provides a combined press-forming and quenchingeffect, whether wholly or locally as the case may be, and with a minimumpossible quench deformation, so that otherwise necessary press-temperingstep for relieving the appreciable deformation developed in thequenching step may be substantially obviated.

In addition, the hardness distribution in the quenched stock is highlyeven and advantageous when relying upon the novel teaching proposed bythe invention.

Under circumstances, the die elements and/or the treating stock may besurface-treated for accelerating or decelerating the quenching effect.For the same purpose, liquid or pulverized medium may be applied ontothe working Surfaces of the die elements, or even onto the processingsurface of the stock per se. An insertion of a metal foil between thework piece and the working surface of the die element. For attaining amore effecting cooling function provided by the coolant, the latter maynaturally be pre-cooled in advance of introduction thereof into the diecooling spaces. A cooling brine may be used under certain occasions.

' What we claim is:

1. A process for press-forming and quenching a diaphragm spring made ofsteel stock, comprising the steps of:

a. heating the diaphragm spring to its austenitizing temperature;

b. placing the heated diaphragm spring on one of two mutuallycooperating die members;

0. cooling said cooperating die members with a liquid cooling medium;and

d. pressing said heated diaphragm spring between the pair of mutuallycooperating die members at a pressure of 6-2,000 kgs./sq.cm. whilerapidly removing considerable heat from the diaphragm spring throughthermal conduction and penetration therefrom to said die members, toform said diaphragm spring to its desired shape while simultaneouslyproviding a quench and hardening effect upon the diaphragm spring stock.

2. The process as claimed in claim 1, wherein said diaphragm spring isheated to a temperature ranging from 750 C. to 950 C. and issimultaneously pressed and quenched to harden said diaphragm spring to ahardness of HRC 55.

3. The process as claimed in claim 1, further comprising the step ofpartially pressing the diaphragm spring under pressure between the pairof said die members to partially press-form the diaphragm spring to itsdesired shape while partially removing considerable heat rapidly from aperipheral ringshaped spring part of the diaphragm spring throughthermal conduction and penetration therefrom to said die members forquenching and hardening said part of the diaphragm spring.

4. An apparatus for simultaneously press-forming and quenching adiaphragm spring made of a steel stock, comprising, an upper die elementhaving a working surface thereon for registration with the correspondingfinished surface of the diaphragm spring, a lower die elementcooperating with said upper die element and having a working surface forregistration with the corresponding opposite finished surface of thediaphragm spring, each of said upper and lower die elements having aninterior space formed therein through which a liquid coolant issubjected to a rapid cooling for quenching and hardening said spring toa predetermined hardness simultaneously with a power actuating meansoperatively connected to said die elements for moving said die elementstowards and away from each other for applying a mechanical pressure of62,000 kgs./sq.cm. on said diaphragm spring stock when said diaphragmspring is pressed between said die elements upon actuation of said poweractuating means to move said die elements towards each other, saidconduit means operatively connected to the interior space in said upperand lower die elements for supplying and discharging said liquid coolantto and from the interior space of each of said die elements, wherebysaid diaphragm spring stock is subjected to a rapid cooling forquenching said spring simultaneously with the pressing of said spring toform said spring to its desired shape under pressure between said cooleddie elements.

5. An apparatus as claimed in claim 4, characterized by each of saidcooperating die elements being formed with a recess partially definingsaid working surface for obtaining the desired local quenching effectupon the diaphragm spring being pressed therebetween.

6. An apparatus as claimed in claim 4, wherein said liquid coolant iscold water.

7. An apparatus as claimed in claim 4, wherein one of said conduit meansis connected between the interior spaces of said upper and lower dieelements for conducting coolants therebetween.

8. An apparatus as claimed in claim 4, wherein said lower die elementfurther comprises a positioning pin located in the center thereof forguiding and positioning a central circular opening formed in saiddiaphragm spring, and said upper die element is formed with acorresponding positioning recess for cooperation with said pin when saiddie elements are moved towards each other.

1. A process for press-forming and quenching a diaphragm spring made of steel stock, comprising the steps of: a. heating the diaphragm spring to its austenitizing temperature; b. placing the heated diaphragm spring on one of two mutually cooperating die members; c. cooling said cooperating die members with a liquid cooling medium; and d. pressing said heated diaphragm spring between the pair of mutually cooperating die members at a pressure of 6-2,000 kgs./sq.cm. while rapidly removing considerable heat from the diaphragm spring through thermal conduction and penetration therefrom to said die members, to form said diaphragm spring to its desired shape while simultaneously providing a quench and hardening effect upon the diaphragm spring stock.
 2. The process as claimed in claim 1, wherein said diaphragm spring is heated to a temperature ranging from 750* C. to 950* C. and is simultaneously pressed and quenched to harden said diaphragm spring to a hardness of HRC
 55. 3. The process as claimed in claim 1, further comprising the step of partially pressing the diaphragm spring under pressure between the pair of said die members to partially press-form the diaphragm spring to its desired shape while partially removing considerable heat rapidly from a peripheral ring-shaped spring part of the diaphragm spring through thermal conduction and penetration therefrom to said die members for quenching and hardening said part of the diaphragm spring.
 4. An apparatus for simultaneously press-forming and quenching a diaphragm spring made of a steel stock, comprising, an upper die element having a working surface thereon for registration with the corresponding finished surface of the diaphragm spring, a lower die element cooperating with said upper die element and having a working surface for registration with the corresponding opposite finished surface of the diaphragm spring, each of said upper and lower die elements having an interior space formed therein through which a liquid coolant is subjected to a rapid cooling for quenching and hardening said spring to a predetermined hardness simultaneously with a power actuating means operatively connected to said die elements for moving said die elements towards and away from each other for applying a mechanical pressure of 6-2,000 kgs./sq.cm. on said diaphragm spring stock when said diaphragm spring is pressed between said die elements upon actuation of said power actuating means to move said die elements towards each other, said conduit means operatively connected to the interior space in said upper and lower die elements for supplying and discharging said liquid coolant to and from the interior space of each of said die elements, whereby said diaphragm spring stock is subjected to a rapid cooling for quenching said spring simultaneously with the pressing of said spring to form said spring to its desired shape under pressure between said cooled die elements.
 5. An apparatus as claimed in claim 4, characterized by each of said cooperating die elements being formed with a recess partially defining said working surface for obtaining the desired local quenching effect upon the diaphragm spring being pressed therebetween.
 6. An apparatus as claimed in claim 4, wherein said liquid coolant is cold water.
 7. An apparatus as claimed in claim 4, wherein one of said conduit means is connected between the interior spaces of said upper and lower die elements for conducting coolants therebetween.
 8. An apparatus as claimed in claim 4, wherein said lower die element further comprises a positioning pin located in the center thereof for guiding and positioning a central circular opening formed in said diaphragm spring, and said upper die element is formed with a corresponding positioning recess for cooperation with said pin when said die elements are moved towards each other. 